> No experience directly, but I've worked on CoCos for years, and they're
The Dragon and Coco are similar on the 'computer' side [1], but the PSU is
rather different. The Dragon has an external transformer box that
connects to a DE9 plug on the back of the Dragon. Inside the Dragon (I've
just looked) there are 2 PCBs. One is double-sided, glassfibre, and
contains the 'computer' stuff (6809, 6883, 6847, RAM, ROM, etc). The
other is single-sided SRBP, and contains the PSU, modulator, and video
output socket (the Dragon has a 3 pin DIN video output, the connections
being audio, ground, composite video in some order).
The 2 PCBs are connected by a short length of ribbon cable with a
plug/socket on the 'computer' board. The PSU circuitry consists of 8
diodes (forming 2 bridge rectifers, one to provide the +5V supply, the
other to provide the +12V, -5V supplies from a centre tapped transformer
winding), a few caps, and 3 3 terminal regulators for the 3 supplies.
There's nothing 'clever' or unconvnentional about it.
[1] The main difference is the printer port. When you've taken over the
lines for the keyboard, sound, etc, there are 3 PIA lines left. The CoCo
uses them to make a bit-banged serial port (2 inputs, one output). The
Dragon uses them to make a centronics port (strobe, busy, acknowledge
IIRC). The Centronics data comes from the same port that provides the
keyboard scan outputs. Since the printer only looks at that data when the
strobe line is active (and it's not active during keyboard scanning), and
since the CPU doens't look at the keyboard inputs when it's printing,
there's no conflict here.
> quite similar. However, if you just want to replace it in the short term,
> try here:
>
> http://www.cadigital.com/computer.htm
>
> Most of the items they sell at that website are insanely expensive, but at
> $35 complete, it's actually rather reasonable... If you're not in the US, I
> dunno what shipping would do to ya...
I assue he's in the UK. The Dragon is much more common over here, I
think. And his domain name looks like a UK amateur radio callsign (am I
right?)
> Dunno if the cassette audio is compatible, but Jeff Vavasour would be the
The cassette format is the same at the bit level, and even at the file
level. The problem is that the BASIC tokens were assigned in a different
order (for what reason %deity only knows!). So ASCII BASIC programs will
load into both machines, as will some machine code programs (provided
they don't use ROM calls that are different on the 2 machines). Tokenised
BASIC programs will load, but won't run, and the listings are garbage!
If you just copy the cassettes to audio CDs, then I can't see why it
won't work (although I really can't see the point of doing this -- if you
want to preserve the recordings I'd not use a CD!). But I would have
thought you could interpret the data on the tape and make a much smaller
file that was essentially a bit image of the 0's and 1's on the tape.
Then convert that back to the right audio format to load it into the
Dragon. The format of the tape data is documented in the CoCo service
manuals, etc.
-tony
Received on Tue Mar 16 2004 - 19:21:27 GMT